Corrosion inhibited acidic solutions containing alkyl hexahydropyrimidine-2-thione and quaternary ammonium compounds



United States Patent 3,457,185 CORROSION INHIBITED ACIDIC SOLUTIONS CONTAINING ALKYL HEXAHYDROPYRIMI- DINE-Z-THIONE AND QUATERNARY AM- MONIUM COMPOUNDS Roy J. Betty and Robert E. Malec, Chicago, Ill., and Charles E. Tippett, Dayton, Ohio, assignors, by mesne assignments, to Armour Industrial Chemical Company, a corporation of Delaware No Drawing. Filed Oct. 14, 1966, Ser. No. 586,667 Int. Cl. C23f 11/04, 11/10, 11/14 US. Cl. 252-391 Claims ABSTRACT OF THE DISCLOSURE Corrosion inhibiting compositions comprising either N-aliphatic hexahydropyrimidine-Z-thione having an alkyl radical containing from 6-22 carbon atoms, or a combination of said thione and a quaternary ammonium compound; and a process for protecting metals in contact with corroding aqueous acidic solutions employing from 10 to 50,000 p.p.m. of such compositions.

This invention relates to new corrosion inhibitor compositions and to a process for protecting metals in contact with corroding aqueous acidic solutions. More particularly it relates to long chain N-aliphatic hexahydropyrimidine thiones in aqueous solutions of acids to inhibit the corrosion of metals in contact with such solutions.

It is well known that the corrosion of metallic substances by the action of aqueous acids such as sulfuric, hydrochloric, phosphoric, sulfamic and citric is a serious problem to industry. This problem is generally experienced in chemical and electrolytic pickling operations wherein baths of aqueous acid solutions are used to remove oxides, carbonates or other scales from metals. It is also experienced in aqueous dipping processes; in plant washout procedures to clean equipment such as indus trial boilers, condensers, heat exchangers and the like with a variety of dilute aqueous acid solutions; in petroleum well operations; and in the storage and handling of aqueous acids and acid containing solutions. A particularly difiicult handling and storage problem is encountered with concentrated phosphoric acid to be used in the manufacture of liquid fertilizers.

It is also known that corrosion inhibitors generally have limited application due to the widely different character of the conditions present in each situation where acid corrosion of metal is a problem. Thus the search for better corrosion inhibitors in a particular area must necessarily be conducted largely on an cmperical basis.

It was therefore surprising to discover a class of corrosion inhibitor compositions which are highly effective under widely varying conditions of use. In one of its aspects this invention relates to corrosion inhibited acidic solutions comprising N-aliphatic hexahydropyrimidine-Z- thiones useful in the cleaning of metallic surfaces. In another of its aspects, this invention relates to corrosion inhibited acidic solutions useful in the manufacture of liquid fertilizers. In still another of its aspects, this in- Patented July 22, 1969 vention relates to corrosion inhibited acidic solutions useful in the storage and transporting of aqueous acids in general.

It is therefore an object of this invention to provide a process for protecting metals from corrosion by aqueous acidic solutions under varying conditions of use.

Another object of this invention is to provide corrosion inhibitor compositions for use in the process of this invention.

Still another object of this invention is to provide corrosion inhibitor compositions in which the solubilizing agent for the corrosion inhibitor cooperates with the inhibitor to increase its effectiveness in protecting metal surfaces.

A further object of this invention is to provide corrosion inhibitor compositions for use in the process of this invention which are effective to inhibit acid corrosion of non-ferrous metals as Well as ferrous metals and do not substantially stain the metals to be protected.

Other objects and advantages and a fuller understanding of this invention will become apparent from the ensuing description and examples.

In British Patent No. 1,067,399 granted Aug. 23, 19 67, there is described a method for the manufacture of long chain N-alkyl hexahydropyrimidine-Z-thiones. In the manner therein described it is possible to obtain compounds of the following structure which we have discovered can be used to effectively inhibit the corrosion of metal by aqueous acidic solutions and to substantially accomplish the objects and aspects of this invention set out above. The formula of the N-aliphatic hexahydropyrimidine-Z-thiones useful to this invention is as follows:

wherein R is an aliphatic hydrocarbon radical having from 6 to 22 carbon atoms. Within the meaning of our ingentiomR may be a straight or branched chain, saturated or unsaturated aliphatic hydrocarbon radical.

in accordance with our invention, it has been found that the corrosive tendencies of aqueous solutions of acid such as sulfuric, hydrochloric, phosphoric, sulfamic and citric may be substantially reduced or mitigated by incorporating into such acids :1 corrosion-inhibiting amount of certain N-aliphatic hexahydropyrimidine-Z-thiones either alone or with known corrosion inhibitors such as a quaternary ammonium compound, and thereafter causing the aqueous acidic solution to contact the metal to be protected.

'The amount of inhibitor necessary in a particular acidic system to obtain optimum inhibition will depend upon environmental circumstances such as the particular metallic substance, the particular acid present in the aqueous corroding solution, the concentration of the acid, and the temperature at which the system is maintained. Generally, we use a concentration range of 10 to 50,000 parts of inhibtor per million parts of aqueous acidic solution. Our preferred range is 50 to 200 parts per million.

The temperatures of metal corroding aqueous acid systerns are quite often found to be in excess of 100 F. and may be as high as 210 F. The concentrations of the acids encountered may be as varying as from .01% to 80% by weight. As would be expected, where the concentration of the acid employed is high and the temperature is elevated, a larger quantity of inhibitor will be required than when lower temperatures and more dilute solutions of acid are employed, wherein the concentration of the inhibitor to produce substantial inhibition of metal corrosion may be proportionately reduced. The N- aliphatic hexahydropyrimidine-2-thiones useful in our process may be added to an aqueous acidic media to inhibit corrosion of metals contacting the media either singularly, in combination with other of the desirable N-aliphatic hexahydropyrimidine-Z-thiones or in combination with known inhibitors. In general, economics will govern the quantity of inhibitor or inhibitor mixtures to be added to any particular system and only that quantity of the inhibitor composition which will produce the result desired will be introduced into the particular system.

In the practice of our invention where ferrous metallic substances are to be contacted by corroding acid media, we prefer to add a corrosion inhibiting composition comprising N-(C C sec-alkyl)-hexahydropyrimidine-2-thione and by weight or less of the particular acid such as sulfuric, hydrochloric, phosphoric, sulfamic or citric. This composition does not substantially stain the metal. A particularly useful corrosion inhibitor composition for ferrous metallic substances contacted by phosphoric acid systems containing up to about 80% by weight phosphoric acid or the salts thereof is the mixture of (A) N-(C C sec-alkyl)-hexahydropyrimidine-2-thione and (B) as a solubilizing substance or agent, a quaternary ammonium compound of the formula R R R R NX wherein R is an aliphatic hydrocarbon radical containing from 6 to 22 carbon atoms, R is an alkyl radical containing from 1 to 3 carbon atoms, R is a hydrocarbon radical selected from the group consisting of R R and (R'O) H wherein R is an alkylene radical having between 2 and 3 carbon atoms, R, is a hydrocarbon radical selected from the group consisting of R R and (R'O) I-I provided that when R is (RO) H, R is (RO) H and x and y are integers having a sum between 2 and 50, and X is a halogen. R within the above definition may be straight or branched chain, saturated or unsaturated aliphatic hydrocarbon.

A typical group of commercially available quaternary ammonium compounds that are within the above definition and are suitable for use in our compositions and process have the trademark Arquad and are manufactured by Armour Industrial Chemical Company, a division of Armour and Company. Preferred quaternary ammonium compounds include:

N-coco-N,N,N-trimethyl ammonium chloride (50% active), the symbol coco standing for a mixture of long chain hydrocarbon radicals derived from coconut oil.

N,N-dicoco-N,N-dimethyl ammonium chloride (75% actice).

N,N-di(di-hydroxy tallow) N,N dimethyl ammonium chloride (75% active), the symbol tallow standing for a mixture of long chain hydrocarbon radicals derived from tallow.

N-(C C sec-alkyl)-N,N,N-trimethyl ammonium chloride. N-(C C sec-alkyl)-N,N,N-trirnethyl ammonium chloride.

Another suitable group of quaternary ammonium compounds within the above definition is an ethoxylated quaternary ammonium salt of the trademark Ethoquad manufactured by Armour Industrial Chemical Company. A preferred ethoxylated quaternary ammonium salt is N methyl N Q coco P N,N polyethyleneoxide (15 moles) ammonium chloride.

No special conditions are necessary to form the inhibitor compositions of a N-(sec-alkyl)hexahydropyrimidine-2- thione plus a quaternary ammonium compound. One component of the mixture is merely added to the other in the desired proportions. Suitable proportions may be obtained with about 25% to about 75% by weight of the N-(sec-alkyl)-hexahydropyrimidine 2 thione in combination with about 75 to about 25 by weight of the solubilizing agent. Our preferred ratio by weight is about 40 to 60% of the N-(sec-alkyl)-hexahydropyrimidine- 2-thione to about 60 to 40% of the solubilizing agent. As with the use of the N-aliphatic hexahydropyrimidine- 2-thiones alone or in combination with each other or known corrosion inhibitors, the amount of the N-(secalkyl) hexahydropyrimidine 2 thione and quaternary ammonium compound corrosion inhibitor compositions which should be incorporated into a particular aqueous acid containing system in order to achieve a metal corrosion inhibiting result can be varied widely and is largely dependent upon the concentration of the acid in the system. A result has been obtained with an effective amount more than 50 parts per million by weight of these compositions, but the preferred concentration range is to 400 parts per million. In general, economics will govem and only that amount of the compositions which will produce the result desired will be introduced into a particular system. Our N (sec alkyl) hexahydropyrimidine 2 thione and quaternary ammonium compound compositions are liquid at room temperatures and are very readily soluble in aqueous acid systems containing a high concentration of phosphoric acid or salts thereof. The compositions, further, do not degrade in such systems and therefore will not leave a residue in the treated system. In addition the compositions, when added to aqueous acid solutions will not substantially stain the metal to be protected.

In order to more fully understand the nature of the compositions of the present process, their characteristics, and the manner in which they may be used, the following illustrative specific examples are provided. The parts used are expressed as percent by weight in the total aqueous mixture unless otherwise specified.

EXAMPLE I N (C -C sec alkyl) hexahydropyrimidine 2- thione, N octyl hexahydropyrimidine 2 thione and 'N dodecylhexahydropyrhnidine 2 thione were tested for corrosion inhibition of 1020 mild steel in contact with aqueous sulfuric acid as follows:

A series of 8 02. bottles containing ml. of acid solution and a quantity of the corrosion inhibitor were placed in an oil bath. The coupons of 1020 mild steel, approximately 1" x 3" x .036 were cleaned in the following manner before initial Weighings: they were tumble in a ball mill with alumdum powder, removed, dipped in hot isopropyl alcohol, then dipped in hot acetone, and air dried. The pre-weighed coupons were submerged in the acid-inhibitor solutions and maintained there at 200 F. for 6 hours. Upon completion of the time period, the coupons were removed (rinsed in hot water and dipped in hot isopropyl alcohol and then in hot acetone, then air dried and reweighed. The concentrations of the acid used were on a weight basis, and the percent inhibitor was based on the weight of the total solution. These are shown in Table I. For comparison, no inhibitor was added in certain instances and this fact is shown in Table 1. Certain known inhibitors were also run under the same conditions and they are identified in Table I. Corrosion rates were calculated on a weight loss basis and expressed in pounds per square foot per day (lb./ft. /day). The results of the tests are set forth in Table I.

TABLE I Percent Percent Corrosion Rate Inhibitor H2804 Inhibitor (lb/itfi/day) None 15 N-(C7-Co sec-alkyD-hexahydropyrimidine-2-thione 15 01 0201 Do 15 03 0160 D0. 15 04 0191 Do. 15 05 0188 D0,- .06 .0179 N-octyl-hexahydropyrimidine-2-thione 15 03 0302 N-dodecyl-hexahydropyrimidine-2-thione 15 03 7768 Dibutyl thiourea 15 03 0790 Do 15 06 0232 Propylene thiourea. 15 01 1. 6973 D o 15 03 1675 Do.---- 15 .05 .2655 Ethylene thiourea 15 01 1. 6139 Do '15 03 9763 Do. 15 05 2073 None N -(C,1Cn sec-alkyD-hexahydropyrimidine-2-tbione 20 006 1534 D0 20 008 1141 20 01 0275 20 03 0193 20 05 0164 None (r) N-(Cv-C sec-alkyl) -hexahydropyrimidine-2-thione 25 01 1217 D0 25 02 0265 25 03 0216 25 04 0234 25 05 0243 I Coupon completely dissolved.

EXAMPLE H weight of the inhibitor compositions and the results of the tests are shown in Table II.

Coupons of stainless steel were placed as described in Example I in bottles containing 15% sulfuric acid and -N-(C ,C sec-alkyl)-hexahydropyrimidine-Z-thioneand there maintained at 200 F. for the times as shown in Table III. As one skilled in the art will recognize, the

build-up of a layer of scale or corrosion upon a metal surface will partially protect the metal surface underneath from further corrosion; thus a greater weight loss by acid corrosion will occur in a short period of time than occurs in a longer period of time. This phenomenon may be observed in the results of this test, shown in Table HI, and it, along with the diiferent types of stainless steel used, accounts for the increased corrosion rates at 2 and 3 hours as compared with 6 hours.

TAB LE II Percent Percent Corrosion Rate Inhibitor H1804 Inhibitor (lb./fl;. /day) None l5 2. 58 N-(Co-Cu sec-alkyD-hexahydropyrimidine-Z-thione... 15 02 0. 0238 Do 15 08 0225 Do 15 04 0236 N (Cu-C14 sec-a y xaf dydropyrimidine-2-thione 15 02 0360 D0 15 03 0272 15 04 0238 N EXAMPLE III TAB LE III Type of Corrosion Stain- Percent Rate less Hours Inhib- (lo/ft. I Inhibitor Steel itor day) None 316 6 0. 0761 N-(Cr-Cn seo-alkyl)-hexahydropyrimidine-Z-thione-.. 316 6 01 0016 D0 316 6 .02 .0013 None 410 3 5. 6308 N -(C Cn sec-alky ahydropyrimidine-2-thione 410 3 01 4. 4983 D 410 3 02 0. 3274 D0 410 3 03 1572 D0 410 3 04 0856 D0 410 3 06 0326 None. 420 2 2. 5627 N-(Crhydropyrimidme-2- 420 2 06 0493 None 430 2 6. 6680 N-(C1C sec-alky hydropyrimidine-2-thione--- 430 2 01 0. 2030 Do 430 2 03 0420 Do 430 2 06 0193 EXAMPLE IV The experimental procedure in this test was the same as that used in Example 1. Coupons of 1020 mild steel were placed .as described in Example I in bottles containing 15 hydrochloric acid and N-(Cq-Cg sec-alkyl)- hexahydropyrimicline-Z-thione and there maintained at 200 F. for 3 hours. The results are shown in Table IV.

TABLE IV Corrosion Rate Percent Percent (lbJitfi/ Inhibitor H01 Inhibitor day) None N 401-09 seo-alkyD-hexahydropyrimidine-2-thione 15 05 0. 1565 D 0 15 15 1101 Do 15 30 1181 l Coupon completely dissolved.

EXAMPLE V The experimental procedure used was the same as that used in Example I. N-(C -C sec-alkyl)-hexahydropyrimidine-Z-thione and difierent aqueous acids were tested for corrosion inhibition of various metals maintained in the corroding acidic solutions at 200 F. for 6 hours. The results are tabulated in Table V.

TABLE V Acid Corrosion god t P t ate ercen ercen lb. it. Acid Metal Inhibitor day) Sulfamic 15%.-. 1020 Mild Steel None 1. 15 Do -d0 01 00954 02 00820 03 0106 04 0124 05 0128 06 0127 None 00845 04 00134 05 00134 06 00136 None 1. 56 04 764 05 254 06 192 None 124 04 0788 05 0830 06 0773 None 000995 04 000908 05 000848 06 000887 None 1. 07 01 0056 02 0046 03 007 3 04 0093 05 0044 06 0044 None 00005 04 000015 05 000063 06 0000144 None 538 04 500 05 481 06 496 None 00097 00074 TABLE V-Continued Corrosion Rate Percent (lb. lftfl/ Inhibitor day) 06 00080 None 286 01 00352 06 00008 None 00084 04 00044 EXAMPLE VI Using the experimental procedure as set forth in Example I, tests were run on mixtures of (A) an N-(secalkyl)-hexahydropyrimidine-2-thione and (B) N-rnethyl-N-coco-N,N-polyethylene oxide moles) ammonium chloric, as corrosion inhibiting compositions for 75% phosphoric acid contacting 1020 mild steel coupons. The tests were run at 120 F. for 48 hours. The compositions used and the results of the tests are set forth in Table VI.

TABLE VI Corrosion Rate (lbJitfl/day) Percent Inhibitor Composition Inhibitor N-(Co-Cn diue-2-thlo and N-methyl-N-coco-N,N-polyethylcueoxide (15 moles) ammonium chloride ll" l4 sec-alkyD-hexaliydrop dine-2-thione and N-methyl-N-coco-N,N-polyethy1eneoxide (15 moles) ammonium chloride N-(C15-C2o scc-alkyD-hexahydropyrimidine-2-thione and N-methyl-N-coco-N,N-polyethylcneoxide N05 moles) ammonium chloride one sec-alkyl)-hcxahydropyrimine 03 EXAMPLE VII Using the experimental procedure as set forth in EX- ample I, tests were run on mixtures of (A) N-(Cq-Cg sec-alkyl)-hexahydropyrimidine 2 thione and (B) N- methyl-N-coco-N,N-polyethyleneoxide (15 moles) ammonium chloride as corrosion inhibiting compositions for 75% phosphoric acid in contact with 1020 mild steel coupons. The tests were run at 50 C. for 48 hours. The mixtures used and the results of the tests are set forth EXAMPLE VIII Using the experimental procedure as set forth in Example I, tests were run on mixtures of (A) N'(C7C9 secalkyl)-hexahydropyrimidine-Z-thione and (B) N-coco N,N,N-trimethyl ammonium chloride (50% active) with 75% phosphoric acid for inhibiting corrosion of 1020 mild steel coupons. The tests were run at 50 C. for 48 hours. The mixtures used and the results obtained are set forth in Table VIII.

TABLE VIII Inhibitor and Percent Inhibitor N-(C1Cn sec-a1kyl)- N -coco-N,N,N-trimethyl Corrosion hexahydropyrimidine ammonium chloride ate -2 th1one (50% active) (IbJttfi/day) EXAMPLE 1X Using the experimental procedure set forth in Example I, tests were run for corrosion inhibition on mild steel coupons using mixtures of (A) N-(C -C sec alkyl)- hexahydropyrimidine-Z-thione and (B) as a solubilizing substance or agent, a quaternary ammonium compound with concentrated (approximately 75 phosphoric acid. Such a mixture is necessary if inexpensive mild steel is to be employed in equipment contacting concentrated phosphoric acid, as is present in the manufacture of liquid fertilizers. The efficacy of our mixtures at low concentrations makes them commercially important for use in the manufacture of liquid fertilizers containing high concentration of phosphorus because our mixtures are soluble at use concentration, are economically attractive will give little or no foaming problem, and they will not substantially stain the metal when added to the acid. The tests were run at 120 F. for 48 hours. The mixtures used and the results of the tests are set forth 1n Table IX.

Inhibitor and Percent Inhibitor N-(CrC sec alkyl)- N-methyl-N-coco-N,N- hexahydropyrimidiue polyethyleneoxide (15 Corrosion Rate -2thione moles) ammonium chloride (lb./tt. /day) N one 361 255 201 181 0065 0305 0430 0382 154 109 0715 0625 0575 0352 0274 N,N-dicoco-N,N-dimethyl ammonium chloride (75% active) N coco-N,N,N-trimetliyl ammonium chloride (50% active) N,N-di(dihydroxy tal1ow)- N,N-dimethyl ammonium chloride (75% active) Inhibitor and Percent Inhibitor N-(C sec alkyl)- N -methyl-N-coco-N,N-

hexahydropyrimidine polyethyleneoxide (l Corrosion Rate -2-thione moles) ammonium chloride (IbJitfl/day) N-(C C14 sec-alkyl)- N,N,N-trimethyl ammonium chloride N-(C Cm sec-alkyl)- N,N,N-trimethyl ammonium chloride N,N-dicoco- N-(Czo-Czz sec-alkyD- N ,N-dimethyl hexahydropyrimidme ammonium chloride -2-thione (75% active) We claim:

1. A process for protecting metals in contact with corroding aqueous acidic solutions which comprises incorporating into said solutions a corrosion-inhibiting amount of an alkyl hexahydropyrimidine-Z-thione having the formula:

CH3 wherein R is an aliphatic hydrocarbon radical having from 6 to 22 carbon atoms, and thereafter causing the said solutions to contact the metal to be protected.

2. The process of claim 1 wherein the corrosion inhibiting amount is from 10 to 50,000 parts of inhibitor per million parts of aqueous acidic solution.

3. Corrosion inhibited acidic solution compositions comprising an aqueous acidic solution and a corrosion inhibiting amount of an alkyl hexahydropyrimidine-Z- thione having the formula:

Wherein R is an aliphatic hydrocarbon radical having from 6 to 22 carbon atoms.

I CH2 wherein R is an aliphatic hydrocarbon radical having from 6 to 22 carbon atoms and (B) a quaternary ammoninurn compound of the formula:

wherein R is an aliphatic hydrocarbon radical containing from 6 to 22 carbon atoms, R is an alkyl radical containing from 1 to 3 carbon atoms, R is a hydrocarbon radical selected from the group consisting of R R and (R'O) H wherein R is an alkylene radical having between 2 and 3 carbon atoms, R is a hydrocarbon radical selected from the group consisting of R R and (RO) H provided that when R is (RO) H, R is (R'O) I-I and x and y are integers having a sum between 2 and 50, and X is a halogen.

7. The composition of claim 6 in which the acid solution is phosphoric acid containing up to about 80% by weight phosphoric acid, and said thione and the quaternary ammonium compound are present in combination in an effective amount more than 50 parts per million.

8. The composition of claim 7 in which the proportions of said thione to the quaternary ammonium compound are from about 25% to about by weight of said thione in combination with about 75% to about 25% by weight of the quaternary ammonium compound.

9. The composition of claim 8 in which said thione is N-(Cq-Cg sec-alkyl)-hexahydropyrimidine-Z-thione and the quaternary ammonium compound is N-methyl-N-coco- N,N-polyoxyethylene (15 moles) ammonium chloride.

10. The composition of claim 9 in which the quaternary ammonium compound is N-coco-N,N,N-trimethyl ammonium chloride.

References Cited UNITED STATES PATENTS 2,947,703 8/ 1960 Larsonneur 252391 X 3,047,510 7/ 1962 Cizek 252-391 X 3,294,695 12/1966 Tippett 252391 X LEON D. ROSDOL, Primary Examiner I. GLUCK, Assistant Examiner U.S. Cl. X.R.

zg gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,457,185 Dated July 22, 1969 lnvenmfls) Roy J. Betty, Robert E. Malec and Charles E. Tippett It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 27, a comma should appear after the word "attractive".

Column 10, in claim 6, line 25, for "R read Slfii'iiii) Mil) SEALED JAN 2 04970 Attest:

Edward M. Fletcher, Ir. WILLIAM E. LER JR. imesting Officer ssioner of Patents &3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 H457, 185 Dated Juli 22, 1969 Inventor(s) Roy J. Betty, Robert E. Malec and Charles E. Tippett It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 27, a comma should appear after the word "attractive".

Column 10, in claim 6, line 25, for "R2" read SlfiiniD Aiiu SEALED JAN 201970 S m Attest:

Edward M. Fletcher, Ir. WILLIAM E. SGHUYLER, JR.

Officer commissioner of Patents 

